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Diffstat (limited to 'ast/erfa/ltp.c')
| -rw-r--r-- | ast/erfa/ltp.c | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/ast/erfa/ltp.c b/ast/erfa/ltp.c new file mode 100644 index 0000000..2b8249c --- /dev/null +++ b/ast/erfa/ltp.c @@ -0,0 +1,140 @@ +#include "erfa.h" + +void eraLtp(double epj, double rp[3][3]) +/* +** - - - - - - - +** e r a L t p +** - - - - - - - +** +** Long-term precession matrix. +** +** Given: +** epj double Julian epoch (TT) +** +** Returned: +** rp double[3][3] precession matrix, J2000.0 to date +** +** Notes: +** +** 1) The matrix is in the sense +** +** P_date = rp x P_J2000, +** +** where P_J2000 is a vector with respect to the J2000.0 mean +** equator and equinox and P_date is the same vector with respect to +** the equator and equinox of epoch epj. +** +** 2) The Vondrak et al. (2011, 2012) 400 millennia precession model +** agrees with the IAU 2006 precession at J2000.0 and stays within +** 100 microarcseconds during the 20th and 21st centuries. It is +** accurate to a few arcseconds throughout the historical period, +** worsening to a few tenths of a degree at the end of the +** +/- 200,000 year time span. +** +** Called: +** eraLtpequ equator pole, long term +** eraLtpecl ecliptic pole, long term +** eraPxp vector product +** eraPn normalize vector +** +** References: +** +** Vondrak, J., Capitaine, N. and Wallace, P., 2011, New precession +** expressions, valid for long time intervals, Astron.Astrophys. 534, +** A22 +** +** Vondrak, J., Capitaine, N. and Wallace, P., 2012, New precession +** expressions, valid for long time intervals (Corrigendum), +** Astron.Astrophys. 541, C1 +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + int i; + double peqr[3], pecl[3], v[3], w, eqx[3]; + + +/* Equator pole (bottom row of matrix). */ + eraLtpequ(epj, peqr); + +/* Ecliptic pole. */ + eraLtpecl(epj, pecl); + +/* Equinox (top row of matrix). */ + eraPxp(peqr, pecl, v); + eraPn(v, &w, eqx); + +/* Middle row of matrix. */ + eraPxp(peqr, eqx, v); + +/* Assemble the matrix. */ + for ( i = 0; i < 3; i++ ) { + rp[0][i] = eqx[i]; + rp[1][i] = v[i]; + rp[2][i] = peqr[i]; + } + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |